1. Field of the Invention
The invention relates to material or panel lifting mechanisms for lifting and unloading material, and particularly large panels or sheets or flat materials, onto a structure such as a building roof.
2. Description of the Related Art
U.S. Pat. No. 4,179,011 issued to Janus Morawski discloses a ladder stabilizing bracing device for attaching to the upper end of a ladder to secure it to the roof of a building. The ladder stabilizing brace comprises a pair of metal arms that attach to the sides of the ladder and extend to a flat rectangular support platform designed to be in contact with a roof. The device disclosed in the '011 patent further discloses the use of a pair of support beams affixed to the ladder's sides and connected to the metal arms to further stabilize the ladder.
U.S. Pat. No. 4,183,423 issued to James P. Lewis discloses a motorized ladder hoist with an adjustable carrier platform that “pivots to horizontal position when the carriage reaches the top.” The ladder hoist is winch operated and contains wheels at the bottom of the ladder to ease transportation to and from a work site. The carrier platform of the hoist travels on rollers along the channel tracks of the ladder. The carrier platform further makes use of stakes to help secure the loads in place during movement up or down the hoist.
U.S. Pat. No. 5,165,501 issued to Howard E. Donahey discloses an adjustable ladder stabilizing device that mounts to the sides of a ladder. The disclosed ladder stabilizer makes use of extension arms that connect to a support platform that transfer weight from the ladder onto a structure. The '501 patent discloses the use of numerous support beams to add rigidity to the ladder stabilizer device.
U.S. Pat. No. 5,180,032 issued to Martiniano Hidalgo discloses a device for securing and stabilizing a ladder to a rooftop or vertical wall. The stabilizing device attaches to the tracks of a ladder and extends a pair of adjustable arms that connect to support anchor platforms designed to engage the roof or vertical wall of a structure.
U.S. Pat. No. 5,743,356 issued to Frank A. Mitchell discloses a ladder stabilizing device that attaches to the tracks and rungs of a ladder to secure the ladder to the rooftop of a building while also protecting the edge and/or gutters of the roof from damage that could be caused by the ladder. The stabilizing device disclosed in the '356 patent teaches extending a ladder away from the roof through the use of a pair of extension arms that connect to a pair of adjustable support arms that attach to a flat support platform designed to be in contact with a roof.
U.S. Pat. No. 5,855,252 issued to Jan William Vrolyks discloses a ladder stabilizing device that attaches to the top end of a ladder. The ladder stabilizing device of the '252 patent mounts to the rungs of a ladder and extends a ladder away from a wall.
U.S. Pat. No. 5,911,287 issued to Ronald L. Campbell discloses a manually operated ladder hoist with a sled that lifts loads up the ladder and a ladder stabilizing attachment. The ladder stabilizing attachment of the '287 patent comprises a brace member that fastens to the rails of a ladder and two rotating arms that extend from the brace member to flat support surfaces designed to be in contact with a rooftop.
U.S. Pat. No. 6,244,381 issued to Timothy E. Ruble discloses a ladder hoist and the use of attaching roller guides to an extension ladder allowing the lifting platform to transition smoothly from one section of the extension ladder to the next section. The '381 patent further teaches the use of a power tool gear and pulley system to lift the carrier platform up the ladder hoist. This publication does not disclose the use of ladder stabilizers or carrier platforms specially designed to securely hold flat rectangular loads.
U.S. Pat. No. 8,002,512 issued to Berle G. Blehm discloses a ladder hoist with an adjustable lift tray. The lifting carrier tray is adjustable to accommodate different desired angles of the tray in relation to the ladder and/or roof pitch. The carrier tray is made up of horizontal and vertical support beams designed to carry flat panel loads.
U.S. Pre-Grant Publication 2005/0139425 by Merle Thomas et al. discloses a ladder stabilizer device that mounts onto the top rungs of a ladder and transfers weight from the ladder onto the horizontal or pitched surface of a roof. The '425 publication discloses the use of adjustable angle extension arms and support beams that connect to a flat support plate designed to be in contact with a roof surface.